Method for determining an image point in an object image

Abstract

A method for determining an image point in an object image comprises the steps of, on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object image has been recorded, weighting the respective picture elements with image signal values corresponding to the respective picture elements or with the reciprocals of the image signal values, thereby to find the center of gravity on the recording medium. A position, at which the center of gravity is located, is determined as the image point in the object image.

I claim: 
     
       1. A method for determining an image point in an object image, which comprises the steps of: i) on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object has been recorded, arraying weighted values as one of image signal values, and the reciprocals of said image signal values so that the positions of said weighted values coincide with the positions corresponding to the respective picture elements,   ii) accumulating said weighted values along each of two different directions on said recording medium and plotting the result cumulative values along each of said two different directions, thereby to find the distributions of the cumulative values along said two different directions,   iii) detecting a coordinate point along each of said two different directions, at which point the cumulative value is approximately one half of the maximum cumulative value, from each of said distributions of the cumulative values, wherein a position on said recording medium, which position is defined by the coordinate points detected along said two different directions, corresponds to the image point in said object image.   
     
     
       2. A method for determining an image point in an object image, which comprises the steps of: i) on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object image has been recorded, performing one of weighting the respective picture elements by storing image signal values corresponding to the respective picture elements when said radiation image has been recorded on a subdivision portion of said recording medium with use of a radiation field stop, and weighting the respective picture elements by storing the reciprocals of said image signal values corresponding to the respective picture elements when said radiation image has been recorded on a substantial portion of said recording medium without use of a radiation field stop, so that the center of gravity of said recording medium can be found; and   ii) determining the center of gravity of the object image, wherein a position, at which said center of gravity is located, corresponds to the image point in said object image, and wherein said recording medium is a stimulable phosphor sheet on which a radiation image has been stored, and said image signal is obtained by a read-out operation wherein said stimulable phosphor sheet is exposed to stimulating rays which cause it to emit light in proportion to the amount of energy stored during exposure to radiation, and the emitted light is detected photoelectrically.   
     
     
       3. A method for determining an image point in an object image, which comprises the steps of: i) on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object image has been recorded, arraying weighted values as one of image signal values corresponding to the respective picture elements, and the reciprocals of said image signal values so that the positions of said weighted values coincide with the positions of the corresponding picture elements,   ii) accumulating said weighted values along each of two different directions on said recording medium, and plotting the resulting cumulative values along each of said two different directions, thereby to find the distributions of the cumulative values along said two different directions,   iii) detecting a coordinate point along each of said two different directions, at which point the cumulative value is approximately one half of the maximum cumulative value, from each of said distributions of the cumulative values, wherein a position on said recording medium, which position is defined by the coordinate points detected along said two different directions, corresponds to a temporary image point,   iv) judging whether or not the image signal value at said temporary image point is within the range of the image signal values which represents the substantial object image, and when it is within said range, said temporary image point is the image point in said object image.   
     
     
       4. A method for determining an image point in an object image, said method comprising the steps of: i) on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object image has been recorded, arraying weighted values, corresponding to the respective picture elements, as one of image signal values, and the reciprocals of said image signal values so that the positions of said weighted values thus arrayed coincide with the positions of the corresponding picture elements,   ii) accumulating said weighted values along each of two different directions on said recording medium, and plotting the resulting cumulative weighted values along each of said two different directions, thereby to find the distributions of the cumulative values along said two different directions,   iii) detecting a coordinate point along each of said two different directions, at which point the cumulative value is approximately one half of the maximum cumulative value, from each of each distributions of the cumulative values,   iv) wherein a position on said recording medium, which position is defined by the coordinate points detected along said two different directions, corresponds to an image point in said object image,   and wherein, after said image signal is detected, calculations are made based on said image signal to find a first representative value which is representative of the image signal values corresponding to the peripheral portion of said recording medium, and a second representative value which is representative of the image signal values corresponding to one of the overall area of said recording medium and approximately the center portion of said recording medium said first representative value and said second representative value being compared with each other, one of the image signal values and the reciprocals of the image signal values is selected for use as the weighted value in said arraying step in accordance with the results of the comparison, and the image point in said object image is determined on the basis of the weighted value.   
     
     
       5. A method for determining an image point in an object image, said method comprising the steps of: i) on the basis of an image signal comprising image signal components representing image information at respective picture elements on a recording medium on which a radiation image including an object image has been recorded, arraying as weighted values, corresponding to the respective picture elements, one of image signal values, and the reciprocals of said image signal values so that the positions of said weighted values coincide with the positions of the corresponding picture elements,   ii) accumulating said weighted values along each of two different directions on said recording medium, and plotting the resulting cumulative weighted values along each of said two different directions, thereby to find the distributions of the cumulative values along said two different directions,   iii) detecting a coordinate point along each of said two different directions, at which point the cumulative value is approximately one half of the maximum cumulative value, from each of said distributions of the cumulative values,   iv) wherein a position on said recording medium, which position is defined by the coordinate points detected along said two different directions, corresponds to an image point in said object image, and   wherein said recording medium is a stimulable phosphor sheet on which a radiation image has been stored, and said image signal is obtained by a read-out operation wherein said stimulable phosphor sheet is exposed to stimulating rays which cause it to emit light in proportion to the amount of energy stored during exposure to radiation, and the emitted light is detected photoelectrically.   
     
     
       6. A method of selecting an image point of an object image recorded on a recording medium, said selected image point representing a center of gravity of said object image and said object image being constituted of a plurality of pictures elements, the method comprising the steps of: converting said object image into electrical signals representative of image values of said plurality of picture elements;   weighting each picture element of said object image by storing the respective electrical signal produced in said converting step corresponding to each picture element when said object image has been recorded on a subdivision portion of said recording medium with use of a radiation field stop, and weighting each picture element of said object image by storing the reciprocal value of the respective electrical signal produced in said converting step corresponding to each picture element when said object image has been recorded on a substantial portion of said recording medium; and   processing said stored electrical signals representing weighted picture elements to determine which one of the stored electrical signals represents the picture element located at the center of gravity of said object image, wherein the image point corresponding to said center of gravity of said object image represents a point within the object image stored on said recording medium.   
     
     
       7. A method as defined in claim 6, wherein said recording medium is a stimulable phosphate sheet for storing a radiation image, and wherein said converting step comprises the steps of: exposing said stimulable phosphor sheet to stimulating rays which cause said stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during exposure to radiation; and   photoelectrically detecting said light emitted from said stimulable phosphor sheet.   
     
     
       8. A method of selecting an image point of an object image recorded on a recording medium, said selected image point representing a center of gravity of said object image and said object image being constituted of a plurality of picture elements, the method comprising the steps of: converting said picture elements into electrical signals representative of image values of said plurality of picture elements;   determining a first one of said electrical signals that corresponds to a first representative value which is representative of the image signal values corresponding to the peripheral portion of said recording medium, and determining a second one of said electrical signals that corresponds to a second representative value which is representative of the image signal values corresponding to one of the overall area of said recording medium and approximately the center portion of said recording medium;   comparing said first and second electrical signals thus determined;   weighting each picture element as a weighted value of said object image by performing one of storing the respective electrical signal produced in said converting step corresponding to each picture element, and storing the reciprocal value of the respective electrical signal produced in said converting step corresponding to each picture element, wherein said one of storing the electrical signal representative of the image signal values and the reciprocals of the image signal values is selected for use as the weighted value in said weighting step in accordance with the results of said comparing step; and   processing said stored electrical signals representing weighted values to located the stored electrical signal corresponding to the center of gravity of said object image, wherein the image point in said object image corresponds to the weighted value found to be the center of gravity.   
     
     
       9. A method of selecting an image point of an object image recorded on a recording medium, said selected image point representing a center of gravity of said object image and said object image being constituted of a plurality of picture elements, the method comprising: converting said picture elements into electrical signals representative of image values of said plurality of picture elements;   weighting each picture element of said object image by storing the respective electrical signal produced in said converting step corresponding to each picture element when said object image has been recorded on a subdivision portion of said recording medium with use of a radiation field stop, and weighting each picture element of said object image by storing the reciprocal value of the respective electrical signal produced in said converting step corresponding to each picture element when said object image has been recorded on a substantial portion of said recording medium;   processing said stored electrical signals representing weighted picture elements to locate the stored electrical signal corresponding to the center of gravity of said object image, wherein the image point in said object image corresponds to the weighted picture element found to be the center of gravity;   comparing an image value of said electrical signal corresponding to the picture element representing the center of gravity of said object image to a predetermined image value corresponding to a predetermined image density; and   judging said picture element representing the center of gravity as a true image point in said object image when said image value is larger than said predetermined image value.